In the context of PV performance analysis and planning, as well as solar thermal or solar heating, the knowledge of the air temperature at ground level (commonly measured at two meters height above ground - T2m) plays an important role. For instance, high temperatures cause higher cooling loads and reduce electricity yields of photovoltaic solar power plants. For many applications it is desirable to have T2m values not just at high temporal, but also at high spatial resolutions, since local influences can be large in the case, for instance, of rough topography. Recently, Zak¿ek and Schroedter-Homscheidt (2009) proposed a parametrization, based on remote sensing data, to provide T2m field of high spatial (1000 m) and temporal (30 min) resolution with an RMSD of about 2 K. It was validated for the regions of France, Germany and Slovenia. The use of remote sensing data was chosen since conventional T2m data are often lacking because the density of the meteorological stations is often very sparse.
The rationale at the basis of the parametrization is that T2m is not driven directly by the sun, but indirectly by the land surface temperature (LST), thus T2m can be parametrized from the LST. Suitable remote sensing sensors are mostly aboard sun-synchronous polar orbiting satellites (e.g. Moderate Resolution Imaging Spectroradiometer - MODIS), resulting in LST retrievals that are available only twice a day for a specific location, depending on cloud cover and geographical latitude. This is not adequate for applications needing continuous T2m measurements. On the other hand, the MSG (Meteosat Second Generation) geostationary satellite carries the SEVIRI (Spinning Enhanced Visible and Infrared Imager) sensor with appropriate split window channels measuring in a temporal resolution of 15 min. The above mentioned parametrization combines SEVIRI and MODIS data and based on an improved temperature-vegetation index (TVX) approach (Prihodko and Goward, 1997) and the energy-balance approach proposed by Meteotest, (2003) and resulting in T2m with high spatial and temporal resolution.
The parametrization was developed to be applicable over large regions without having to take into account differences in the land cover type¿s surroundings the meteorological stations. A wide variety of land cover types was employed in the test data set. However, to increase the accuracy of the T2m measurements, the parametrization might be further refined considering areas with land cover different from the actual validation areas (e.g. the Andalucía region in Spain). The purpose of this study is to extend the parametrization approach validation in view of a recalculation of its coefficients.
Most satellite data used in the study are SEVIRI-MSG data and are processed by the Land Surface Analysis Satellite Applications Facility (LSA-SAF). The LSA-SAF LST, down-welling surface short-wave radiation flux (DSSF), and surface albedo (AL) products are considered together with MODIS 16-day composites of normalized differential vegetation indexes (NDVI) ones, at 1000 m spatial resolution, processed by NASA.